Electrostatic recording systems are utilized in equipment such as facsimiles, computer input-output systems, high speed graphic reproduction systems, and the like to fix the electronic signal received by the equipment in a form which people can interpret. The signal is fixed on electrostatic recording materials that comprise a highly dielectric layer, that serves as an electric-charge-retentive layer, and an electrically conductive substrate that supports the dielectric layer. Electrostatic images of electrical signals formed on the dielectric layer are conventionally made visible with a developer comprising a toner and a carrier that has a polarity opposite to the polarity of the electrostatic image charge.
The dielectric layer is conventionally produced from a pigmented dispersion applied onto the conductive substrate comprising high molecular weight materials and pigments dissolved in organic solvents.
Representative high molecular weight materials include polystyrenes, polyacrylates, polyvinylidene chlorides, polyvinyl acetates, polyvinyl acetals, nitrocelluloses and silicone resins The pigment assists adherence of the toner to the electrostatic recording material. Representative pigments include calcium carbonate (atomite), kaolin clay and the like. Representative organic solvent are acetone, toluene, benzene, methylethyl ketone, and the like. However, the use of such organic solvents is disadvantageous because of the flammability, health hazards and expense thereof.
To avoid these disadvantages of organic solutions some attempts have been made to use aqueous coating compositions to form the dielectric layer on the conductive substrate. However, the electrical ions of the electrically conductive agent on the surface of, or in, the conductive substrate can migrate into the dielectric coating produced from the aqueous coating composition which results in the degradation of the electrostatic characteristics of the dielectric layer. Thus, using such aqueous compositions involves serious defects such as deterioration in the charge retention and dielectric properties of the dielectric layer which results in poor print densities.
Attempts have been reported wherein a barrier layer is formed between the electrically conductive layer of the conductive substrate and the dielectric layer to prevent migration of the electrically conductive agent into the dielectric layer. However, a barrier layer results in (1) an economic disadvantage due to the additional step of applying the layer, and (2) a functional defect due to the decrease in recording sensitivity of the dielectric layer.